That's in contrast to earlier studies that suggested the widely used nicotine products are harmless during pregnancy.

"There was a general feeling that nicotine replacement therapy was safe," said Alison Holloway, a professor at McMaster University in Hamilton, Ontario, who was not involved in the new work.

"I think what people are trying to say now is it may still be a better option than smoking during pregnancy, but it may have other consequences that haven't been explored yet," she added.

Smoking, on the other hand, is known to have negative consequences on babies, and previous research has shown that smoking while pregnant is tied to an increased risk of colic.

Colic is excessive crying in babies -- at least three hours a day for more than three days a week and lasting more than three weeks in a row.

While it eventually goes away, it can be hard on parents and there is no known cure.

The lead author of the study, Dr. Ioanna Milidou at Aarhus University Hospital Skejby in Denmark, said she wanted to see if it was the nicotine itself that might be responsible for the higher risk of colic among babies with mothers who smoked.

She and her colleagues gathered information on 63,000 moms who had had a baby between 1996 and 2002.

About 15,000 of the moms had smoked while pregnant, roughly 1,200 had used some form of nicotine replacement and had smoked at some point in their pregnancy, and 207 moms had used nicotine replacement therapies only.

About seven percent of babies whose moms never used nicotine had colic.

In comparison, nine percent of babies whose moms smoked and 11 percent of babies whose moms used nicotine replacements had colic.

Smoking during pregnancy is believed to take a toll on the baby's health, but there have been very few studies of nicotine alone in humans, Milidou said.

"We have a lot of evidence from animal studies...that nicotine compromises the development of critical neuro-pathways and maturation signals in the developing brain," she told Reuters Health.

Milidou said that while the rates of colic are higher among babies exposed to nicotine, her results don't prove that nicotine is responsible.

"One of the shortcomings of my study is we don't have enough data to say how much (nicotine) these women were using," she said.

She and her colleagues note in their report in the journal Pediatrics that nicotine replacement therapy has become more commonly used among pregnant women.

"There's been lot of focus on helping pregnant women to quit smoking," she said.

There are alternatives to using nicotine replacement therapy to try and quit, such as successful behavioral interventions.

But Milidou said that if the alternative to using nicotine replacements is to smoke, it's probably better to avoid the cigarettes because of all the known risks of smoking.

"I think they were very careful not to say (in the study) that you should stop using it, but that you really need to consider whether there are other aspects of nicotine replacement therapy that are affecting the health of the offspring," Holloway told Reuters Health.

Milidou's group calls for more research on the effects of nicotine in babies.

SOURCE: bit.ly/wODi7y Pediatrics, online February 20, 2012.

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